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According a PopSugar interview with Vikander’s trainer Magnus Lygdback, the 29-year-old actress began the low-carb, high-fat regimen two months before filming started. The goal in Vikander’s case was to maintain muscle while shedding fat (though we can’t imagine whence the lithe former ballerina found any to shed).

“Since we were traveling so much over the holidays, we decided the keto diet would be best because it’s easier to control the macros that way,” Lygdback said.

And by macros, he means the macronutrients — as in carbohydrates, protein and fat. In a typical keto diet, 60 to 75 percent (or more) of calories come from fat, 15 to 30 percent from protein and 5 to 10 percent (or less) from carbs.

A ketogenic diet is high in fat and low in carbohydrates.Photo Credit: Warner Bros

Vikander ate a lot of fish and seafood as a protein source and “MCT oil, avocado, and coconut oil as a fat source,” said Magnus. She also loaded up on keto-friendly veggies (so, basically, just greens) while keeping her carb count under 25 grams a day. (For keto newbies, the low carb count is what’s supposed to trigger your body to convert stored fat into ketones to burn for energy.)

“It’s always tricky the first couple of days, but [Vikander’s] willpower is just unbelievable, and she didn’t complain, even though I could see she was struggling a little bit,” said Magnus. “She kept on bringing it every day.”

Of course, it takes more than diet — no matter how strict — to get a ripped physique. For seven months leading up to filming, Vikander also hit the gym with Lygdback five to seven days a week.

Lygdback (who will train Gal Gadot for the “Wonder Woman” sequel) told Popsugar, “I like to switch it up, so we did everything from squatting heavy and doing deadlifts to pull-ups, push-ups, training with machines, training with body weight, plyometrics, explosive training.”

The results? Alicia put on 12 pounds of muscle and was rewarded with six-pack abs that, if you missed seeing, are really worth a look.